It was me! I hid the question because, even if I asked my answerer to edit it, he didn't tell me what they were actually based on. All me told me was what their name etymology was; what their names come from.

Ultra Moon Dex Entry: When stone walls started moving and attacking the brute's true identity was this mysterious life-form, brings to mind an Ultra Beast.

Blacephalon's name comes from a play on the word "Blasphemy", "Blaze" or "Blast", and the Greek word "Cephalos" (κεφαλος), which means head.

It's Japanese name, "Zugadon", literally means "Head Goes Boom". It's French name, "Pierroteknik", is a misspelling of "Pyrotechnic". It's German name, "Kopplosio", is a mix of "Kopf (head)" and "explosion".

Due to its clown-like appearance and strange movements, several fans compared Blacephalon to Stephen King's novel character Pennywise.
It has some characteristics of fireworks. It is also based on a clown.